A month after the March 11, a 9.0 earthquake triggered a 30-foot tsunami that damaged several nuclear reactors in northeastern Japan, causing the country's worst crisis since World War II, a 7.4 temblor shook the country again.

Members of the Japan Grounf Self-Defense Force search a tsunami damaged part of Ofunato, Japan on Tuesday, March 15. Two search and rescue teams from the US and a team from the UK with combined numbers of around 220 personnel, searched damaged areas of the town of Ofunato for trapped survivors Tuesday in the aftermath of the earthquake and tsunami.

A powerful tsunami triggered by the earthquake sweeps away cars and homes and knocks out regular and backup cooling systems at the six-reactor Fukushima Daiichi nuclear power plant. Several reactors are affected.

The government orders everyone within a three kilometer radius of the plant to leave the area.

Japanese authorities report that a fire at the Onagawa nuclear power plant is extinguished.

Day 2 – Saturday, March 12

A blast caused by a pressure buildup blows the roof off the containment structure of the Fukushima Daiichi plant's Unit 1 reactor, but reports say the nuclear fuel rods are not affected. Four workers are reported injured.

Residents within a 6-mile radius of the plant are evacuated. Kyodo news agency estimates that 20,000 people are being evacuated.

Workers begin injecting seawater and boric acid into the reactors in what experts say is a last-ditch attempt to prevent a meltdown after the backup cooling systems for reactors 1 and 3 fail completely.

A company spokesman states that the radiation released thus far does not pose a health risk to humans.

The cooling system in reactor 2 fails and more radioactive steam is released.

The government evacuates more than 200,000 residents from homes within a 20-kilometer (12.4-mile) radius of the plant and tests 160 people for radiation exposure, authorities said Sunday.

IAEA rates the accident as a level four out of seven on the scale of international nuclear disasters. Three-Mile-Island was rated a five, Chernobyl a seven.

Meanwhile, in southwestern Japan, Shinmoedake volcano erupts for the second time in 2011, sending ash and rock more than two miles into the air. Analysts say it was the biggest volcanic activity there in 52 years.

An explosion caused by pressure buildup blows away the roof and walls of the building housing the Fukushima Daiichi plant's No. 3 reactor and injured 11 people. The plant's No. 2 reactor loses its cooling capabilities after the explosion. Workers begin injecting seawater and boric acid into that reactor.

An explosion hits Fukushima Daiichi's No. 2 reactor in the morning. Readings indicate some damage to the No. 2 reactor's suppression pool, a donut-shaped reservoir at the base of the reactor's containment vessel.

A fire is ignited in the No. 4 reactor building Tuesday, but is later put out, according to officials.

The plant is emitting as much radiation in one hour as it normally would in six months, but government spokesman Yukio Edano says: "The possibility that a large amount of radiation has been released is low."

Nuclear Regulatory Commission Chairman Gregory Jaczko indicates in remarks to a House committee that the US believed the damage at the Fukushima Daiichi nuclear power complex was even graver than Japanese officials had outlined in public.

Day 7 - Thursday, March 17

The US ambassador in Japan issues a statement to American citizens living within 50 miles of Fukushima to evacuate.

Workers begin to try to use a water cannon to blast water into the No. 4 building.

US authorizes voluntary departure from Japan of family members of diplomatic staff, and later US citizens.

Three out of the six reactors at Fukushima are relatively stable, say officials.

TEPCO said it has started work to connect outside power cables to the plant and that electricity could be connected soon.

Chief Cabinet Secretary Yukio Edano said Friday that residents living between 20 and 30 km from the Fukushima nuclear power plant are being urged to “voluntarily evacuate.” Residents in those areas had been previously told to stay indoors.

Edano stressed that current radiation levels in the area do not necessitate immediate evacuation.

Workers began pumping fresh water into the Unit 1 and Unit 3.

White smoke continues to be seen coming from the Unit 2 and Unit 4 reactors.

Small amounts of plutonium have been discovered outside Fukushima's reactor buildings. The radioactive material was found in five separate soil samples. External exposure poses little health risk, according to the US Environmental Protection Agency.

Day 19 - Tuesday, March 29

Focus remains on Unit 2, where workers are attempting to contain a possible water leak.

Officials say plutonium found in the soil near the plant could mean the reactors experienced a partial meltdown.

Day 20 - Wednesday, March 30

Tepco announces it will decommission four of the six nuclear reactors at Fukushima Daiichi

Radioactive water in and around reactor buildings is delaying cooling efforts.

Japan's nuclear safety agency says the radioactive iodine at 3,355 times the legal limit does not pose a health threat.

Week 4Day 22, Friday, April 1

Researchers say that the tsunami reached as high as 29.6 meters in Ofunato City, Iwate. It was previously thought the highest wave reached only to 20 meters.

The Nuclear safety agency says radioactive material 4,385 times the legal limit has been found in sea water near the plant.